1. Field of the Invention
The invention relates to environmental chambers, and particularly to environmental chambers which utilize thermoelectric heat pumping devices to maintain a temperature in a thermal compartment of the environmental chamber at a preselected value.
2. Description of the Prior Art
Conventional environmental chambers for thermal testing of various devices or substances have metal inner and outer surfaces, use fiberglass insulation, have large temperature ranges, typically from approximately one hundred degrees centrigrade below zero to over three hundred degrees centigrade above zero. Present environmental chambers typically weigh at least one hundred pounds because of their metal construction and heavy refrigerating mechanisms. The metal construction and use of fiberglass insulation are necessary because of the high temperatures which can be produced by the environmental chambers. Some presently available environmental chambers utilize liquid CO.sub.2 contained in heavy metal bottles for achieving low temperatures, bringing the total weight of the system to at least several hundred pounds. If a refrigeration compressor unit is used, the entire system typically weighs at least 250 pounds. Prices of presently known environmental chambers are in the range of at least $800.00 to $2,500.00 for a simple "temperature chamber". Typically, presently known environmental chambers include an analog control that is utilized to "set" a particular desired temperature in the range from approximately minus 100 degrees centigrade to plus 300 degrees centigrade. It usually is impossible to precisely set a desired temperature with such an analog control. The prior art environmental chambers are completely non-portable, are incapable of operating from typical voltages, such as twelve volt batteries, available on vehicles "in the field". Furthermore, prior environmental chambers that utilize electrical resistive heating elements and compressor-type refrigerating systems usually generate large "surges" in the electrical supply system when a heating element or a refrigeration unit thereof is switched on or off during normal operation.